The final lithography step in printed circuit manufacturing is mask patterning. Although a variety of ultraviolet curable materials could be used, a negative photoactive soldermask material is typically patterned using an ultraviolet (UV) source and a hard mask. With reference FIG. 1(a), a printed circuit, such as a printed circuit board 10, with a copper pattern 12 and a soldermask layer 14 disposed thereon is shown. Runout is measured. In addition, an appropriate pattern mask 16 is selected and positioned for a patterning operation.
Typically, the soldermask layer is coated, or otherwise formed, on the printed circuit board 10 and the combination is then soft baked. The mask 16 is then applied. As shown in FIG. 1(b), the printed circuit board 10 is exposed to, for example, ultraviolet light through the pattern mask 16. In the case where a negative photoactive soldermask is used, areas that are not masked, such as areas 18, in the soldermask are cross-linked during the exposure. The pattern mask 16 is then removed and, as shown in FIG. 1(c), the arrangement is developed so that the areas of the soldermask that were not cross-linked are removed during development. In this process, the copper pattern 12 is exposed so that electrical contact can be established.
However, in using methods such as that shown in FIGS. 1(a)-1(c), various difficulties arise. For example, because the run-out varies and is large using this type of technique, several different “stretched” masks 16 are used to match layer-to-layer alignment. This limits the layer-to-layer accuracy and, for cases where the run-out is very large or non-uniform, the printed circuit board 10 typically needs to be scraped. In addition, using multiple masks 16 increases run time and process errors.
Also, systems that use wax patterning are known. However, these systems require that extra steps be taken in the process to remove the wax, which can be difficult.
Thus, a method to individually and digitally stretch a mask without significantly changing the current industry process is desired. Such a system would improve yield, productivity and reduce linewidth tolerances.